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Old 08-01-2020, 12:32 PM   #1
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Which Battery is better - or neither?

My boat has 2 batteries. I alternate use based on even and odd days. If an odd day I use battery #1, even I use battery #2. Battery 2 is starting to slow down in it's cranking ability but otherwise still functions. I use a trickle charger to keep both batteries charged over the winter and this has extended my battery lives from 3 yrs to 8 yrs. Battery #2 is an 8 yr old Group 24 Interstate battery and has a 12.4V reading when it is at rest. My battery #1 returns 12.8V at rest so it is good.

My Airstream has the factory solar and included 2 Lifeline Group 24 AGM batteries. They are 2 years old. Recently, I tested the voltage at rest for each. 1 battery had 12.9V at rest and the other 12.2V. I had thought the batteries were doing OK but I thought AGM's should be doing better than what they had been. Turns out the bad battery was the issue. Lifeline sent me a prorated replacement battery that matches the 12.9V at rest of my other battery. The AGM batteries have 800 cranking amps, as does my Interstate non-AGM battery.

I had been planning on replacing my boat battery #2 at some point. I was wondering if the old AGM could be used as a replacement battery for it? I was expecting the AGM to return a higher voltage that the Interstate but it did not. I have heard that AGM's are better long term than non-AGMs. I realize the age of my Interstate is at/near the end.

My question - Is a 2 year old AGM battery that returns 12.2V at rest better than a 8 yr old non-AGM battery that returns 12.4V at rest? Or, are both of these batteries ones that should be scrapped?
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Old 08-01-2020, 03:33 PM   #2
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If the two boat batteries are over eight years old, I’d replace both,,,Costco has them on sale for under $100 each
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Old 08-01-2020, 03:36 PM   #3
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How long are you waiting to check voltage after disconnectIng power? Should wait a couple hrs to get a true reading
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Old 08-01-2020, 03:51 PM   #4
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Originally Posted by Spinonedad View Post
How long are you waiting to check voltage after disconnectIng power? Should wait a couple hrs to get a true reading
I waited a full day. The AGM will get up to 12.7 after a charge but always settles back to 12.2V. I just thought AGMís have more cycles than regular lead acid batteries so it should hold its 12.2 longer than the interstate can hold its 12.4. However; I donít think the 12.2V will deliver what I need.

Just thought Iíd throw it out there for persons more knowledgeable than I.
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Old 08-02-2020, 09:40 AM   #5
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Hi

The right way to manage the batteries in the AS is to keep them in parallel all the time. You never use them / charge them one at a time in an AS.

If you replace one battery in a pair, you really should also replace the other one. Batteries with different wear histories will not balance well. The result is that one will do most of the work and wear out quickly ....

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Old 08-02-2020, 11:03 AM   #6
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You need a computer charger with 2-4-8 volt charge selections, battery type selection, and desulfator. I have one made by Battery Minder. It will bring old AGMs back in just a few days. My boat's cranking battery (an Optima 24) was getting weak, but the desulfator saved it. AGMs really ought to read 13.2v resting, if in good health. Also, GM has recommended only replacing one parallel battery at a time as long as the the other(s) test OK. I have been doing that for 8 or 10 years now will good results. Its much cheeper too.
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Old 08-02-2020, 02:43 PM   #7
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Iíve been stressing over my batteries and maintaining the right charge. My 2020 GT 30í is 130 miles away at a RV park in the forest. I have neighbors checking a voltage meter i installed. Iíve learned voltage is not accurate. Right after i bought it the convertor went out and ruined our food. We go up every two weeks.

So after much research Iíve come up with the following solution.

I have a hotspot always on (1/4 mile from cell tower). I added a rvwhisper box connected to hotspot. I built the attached gizmo. 3 PowerMon Bluetooth units. One for total RV amp/watt draw. One for Solar only, last one inverter. I intend to Velcro to the underside of battery box. Cables may need to be shorter but Iíll deal with that when i get there. I used 4, 6, 10, 12 and 16 gauge wire based on max amp draw. I have a 60 amp fuse in the house battery. Both inverter and solar are protected in the trailer. All connections are appropriate size crimped and heat shrink. Iíve tested the connection at home with my car. Signal going thru hood, 2 walls and window i can be 25 feet away. I intent to put the rvwhisper under the front sofa. 4 feet from PowerMon devices.

Wish me luck!

I can monitor it all from a phone app hundreds of miles away. It will also send me a text when the fridge gets too hot or shore power quits. Once i analyze the data i will know for sure how long the solar will keep it up. Since i have a 12v fridge Iím hoping 20-24 hours. Lots of sun up there. Plenty of time to get up and run generator. Iíll keep you posted.

Jim
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Old 08-02-2020, 03:11 PM   #8
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LiON is the future for all batteries
the next set will be soild state Li models in 2-5 years
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Old 08-02-2020, 04:10 PM   #9
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If possible, can afford, when your boat batteries go bad, replace them with the trailer batteries. Since you have two, you can use them until they are really shot. Put a 100ah lithium in your trailer. Approximately doubles your useable ah.
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Old 08-02-2020, 04:49 PM   #10
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12.2 indicates onset of a bad cell, 12.4 could be excessive sulfacation. I'd put it on a charger that can maintain 14.6-14.8 V for 12 hours and check it again. You may be able to get some more life out of it.

The trickle charger doesn't deliver enough current to prevent or reverse acid stratification and sulfacation.
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Old 08-04-2020, 06:26 AM   #11
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12.2 indicates onset of a bad cell, 12.4 could be excessive sulfacation. I'd put it on a charger that can maintain 14.6-14.8 V for 12 hours and check it again. You may be able to get some more life out of it.

The trickle charger doesn't deliver enough current to prevent or reverse acid stratification and sulfacation.
Thanks Brian!
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Old 08-12-2020, 09:54 AM   #12
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I used to have a large sailboat with a 700 amp hour battery bank. Over the 17 years I had the boat I read a lot about battery maintenance, life, etc. I found that no matter what I did I never got more than 7 or 8 years out of a battery. Also, I think consensus is that when you replace one in a bank you replace them all, unless you just happened to get one bad one in a fairly new set of batteries, if their age, capacity, etc is much different the bad/old ones bring the whole bank down.


I also invested in a very good battery tester, an Auto Meter, that can load test the batteries along with giving voltage, etc. Although it cost the better part of $500, I think it was money well spent.


As far as AGM vs wet cells, I think there is little advantage of an AGM over a PROPERLY maintained wet cell.
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Old 08-12-2020, 10:09 AM   #13
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As far as AGM vs wet cells, I think there is little advantage of an AGM over a PROPERLY maintained wet cell.

You properly emphasized properly. The problem is that almost no one properly maintains wet cells. If you were involved in the battery rituals on a submarine, you know what properly means. So, accepting that almost no one does that with our 12v batteries, AGM has huge advantages for batteries that are not or do not require the loving care of wet cells.

Larry
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Old 08-12-2020, 11:36 AM   #14
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Quote:
Originally Posted by lsbrodsky View Post
As far as AGM vs wet cells, I think there is little advantage of an AGM over a PROPERLY maintained wet cell.

You properly emphasized properly. The problem is that almost no one properly maintains wet cells. If you were involved in the battery rituals on a submarine, you know what properly means. So, accepting that almost no one does that with our 12v batteries, AGM has huge advantages for batteries that are not or do not require the loving care of wet cells.

Larry
I agree with both of these statements. I still have wet cells and pay much attention to the care and feeding of them. The cost/benefit ratio of the advantage of agm (weight to power ratio, less maintenance, slightly deeper discharge) etc isn't wort the cost difference FOR MY USAGE LIFESTYLE.
That said, I will be switching to agm next year (probably) because I have a need to bring my bank inside the living space for a few reasons.
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Old 08-12-2020, 02:32 PM   #15
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Most RV and boat batteries have only a 1 year warranty, but car batteries have up to 5 years or more. I'm guessing it's because car batteries get exercised on a regular basis, daily in most cases.

My AS has a solar panel on top, which keeps them charged, but even after buying new Lifeline AGMs for it, I was disappointed in their lifespan. I didn't take advantage of the 5 year warranty and I kick myself for that (thought it was a 1 year warranty and 5 years has passed). At present, they will hold a charge at 12.4 - 12.5 volts. They are still serviceable since we don't boondock.

The next time I buy batteries for the AS it will be regular deep cycle batteries, probably Duracell, which are made by Deka. Just a 1 year warranty but my Deka trolling batteries are on season 3 and still hold a full charge.

After having several starting and trolling motor batteries go bad while in storage, I got a timer for my on-board 3-bank charger, 15 amp on each bank. I set the timer for twice daily, morning and evening, 15 minutes each. On Fridays there's an additional 30 minute charge. The charger checks each battery and will start charging or go into maintenance mode as required. The timer shuts everything off after the programmed time is up. I check the acid level about 4 times a year, adding only distilled water. They are always plugged in unless I'm fishing.

As far as longevity is concerned, I still have the Panasonic group 27 battery that came in my '04 4Runner, fall of 2003. It still holds a charge at 75% after 27 years. Wish we could get Panasonic batteries here.
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Old 08-13-2020, 06:00 AM   #16
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Just to close out my questions as the OP.

I took the AGM to a battery shop to test and it failed when load was applied. Re; the wet cell battery, even though I can ďget byĒ with it I will replace due to age and donít want it pulling down the other pre-maturely.

Thanks for all the advice from all!
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Old 08-13-2020, 09:22 AM   #17
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My question - Is a 2 year old AGM battery that returns 12.2V at rest better than a 8 yr old non-AGM battery that returns 12.4V at rest? Or, are both of these batteries ones that should be scrapped?
I would scrap both batteries.
Both batteries show that they have sulfated to the point where they no longer can maintain a good charge. Lead acid batteries die quickly when they go.

12.4V indicates that the battery has reduced to 70% capacity. Since lead acid/AGM should not be discharged below 50% - that provides you with a usable 20%. If they are Grp24 80Ah batteries, that means you have at most 16 Ah before you drop to 12.1V. (50% SOC)

12.2V indicates that the battery has reduced to about 58% capacity. Since lead acid/AGM should not be discharged below 50% - that provides you with a usable 5.8%. If they are Grp24 80Ah batteries, that means you have at most 4.64 Ah before you drop to 12.1V. (50% SOC)

I have attached a couple of charts for your review. The difference in voltage between flooded and AGM is not significant.

https://modernsurvivalblog.com/alter...-charge-chart/

https://priuschat.com/threads/weak-12v-battery.139851/
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Old 08-13-2020, 10:30 AM   #18
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Originally Posted by waninae39 View Post
LiON is the future for all batteries
the next set will be solid state Li models in 2-5 years
There are a lot of new technologies that have promise. When they work out the kinks - it will be nice. In the meantime, current Li-ion technology is getting better and safer. The Nickel cobalt lithium are the batteries that can catch fire and explode. That is what the media likes to extort. Considering the millions of NCM lithium batteries out there - they have a pretty good safety record.
The safest lithium ion batteries are the LiFePO4 and lithium titanate. LT batteries are expensive and therefore not common. Lithium phosphate are inexpensive to manufacture. Other lithium chemistry have the potential to catch fire or explode. Lithium iron phosphate have a lower energy density which is not prone to fire or explosion.
You have a lot of LFePO4 options.

Potential suppliers include:

AMPS Lithium
https://lithiummarinebattery.com

LiFeBlue Battery
http://www.lifebluebattery.com

ReLion
https://relionbattery.com

GoPower
https://gpelectric.com/product-category/batteries/

Battleborn
https://battlebornbatteries.com

Renogy
https://www.renogy.com

SmartBattery
https://www.lithiumion-batteries.com
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